Feedthrough rejection for optomechanical devices

ABSTRACT

An optomechanical device for producing and detecting optical signals comprising a proof mass assembly, one or more laser devices, and a circuit. The one or more laser devices are configured to generate a first optical signal and a second optical signal. The circuit is configured to modulate, with an electro-optic modulator (EOM), the second optical signal, output the first optical signal and the second optical signal to the proof mass assembly, generate a filtered optical signal corresponding to a response by the proof mass assembly to the first optical signal without the second optical signal, and generate an electrical signal based on the filtered optical signal, wherein the EOM modulates the second optical signal based on the electrical signal.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under N66001-16-C-4018awarded by SPAWAR Systems Center Pacific. The Government has certainrights in the invention. This material is based upon work supported bythe Defense Advanced Research Projects Agency (DARPA) and Space andNaval Warfare Systems Center Pacific (SSC Pacific).

TECHNICAL FIELD

This disclosure relates to optomechanical devices, such asaccelerometers configured to measure acceleration using an opticalsignal.

BACKGROUND

Optomechanical devices include devices for detecting acceleration,velocity, vibration, and other parameters. For example, in anoptomechanical accelerometer, the resonance frequency of a mechanicalstructure is shifted under acceleration in the optomechanical device.The mechanical resonance frequency can be read out with an optical fieldby applying near-resonant light to the structure's optical resonance andmeasuring the transmitted or reflected optical signal.

SUMMARY

In general, this disclosure is directed to devices, systems, andtechniques for reducing drive feedthrough in optomechanical devices. Asused herein, drive feedthrough may refer to the portion of the opticaldriving field which leaks into the detection path and is independent ofacceleration. Drive feedthrough may limit the ultimate noise floor andhence performance of the optomechanical device. For example, a circuitmay be configured to output the first optical signal as a driving fieldto drive a mechanical response to a proof mass assembly and output thesecond optical signal as a sensing field to the proof mass assembly todetect one or more of a modulation in phase or frequency of mechanicalvibrations in the proof mass assembly.

In one example, an optomechanical device for producing and detectingoptical signals includes a proof mass assembly; one or more laserdevices configured to generate a first optical signal and a secondoptical signal, wherein the first optical signal comprises a frequencydifferent than a frequency of the second optical signal; and circuitryconfigured to: modulate, with an electro-optic modulator (EOM), thesecond optical signal; output the first optical signal and the secondoptical signal to the proof mass assembly; generate a filtered opticalsignal corresponding to a response by the proof mass assembly to thefirst optical signal without the second optical signal; and generate anelectrical signal based on the filtered optical signal, wherein the EOMmodulates the second optical signal based on the electrical signal.

In another example, a method for producing and detecting optical signalsincluding: generating, by one or more laser devices, a first opticalsignal and a second optical signal, wherein the first optical signalcomprises a frequency different than a frequency of the second opticalsignal; modulating, by an electro-optic modulator (EOM) of circuitry,the second optical signal; outputting, by the circuitry, the firstoptical signal and the second optical signal to a proof mass assembly;generating, by the circuitry, a filtered optical signal corresponding toa response by the proof mass assembly to the first optical signalwithout the second optical signal; and generating, by the circuitry, anelectrical signal based on the filtered optical signal, wherein the EOMis configured to modulate the second optical signal based on theelectrical signal.

In another example, an optomechanical system for producing and detectingoptical signals includes one or more laser devices configured togenerate a first optical signal and a second optical signal, wherein thefirst optical signal comprises a frequency different than a frequency ofthe second optical signal and a circuit configured to: modulate, with anelectro-optic modulator (EOM), the second optical signal; output thefirst optical signal and the second optical signal to a mechanicalassembly; generate a filtered optical signal corresponding to a responseby the mechanical assembly to the first optical signal without thesecond optical signal; and generate an electrical signal based on thefiltered optical signal, wherein the EOM modulates the second opticalsignal based on the electrical signal.

The summary is intended to provide an overview of the subject matterdescribed in this disclosure. It is not intended to provide an exclusiveor exhaustive explanation of the systems, device, and methods describedin detail within the accompanying drawings and description below.Further details of one or more examples of this disclosure are set forthin the accompanying drawings and in the description below. Otherfeatures, objects, and advantages will be apparent from the descriptionand drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an electro-opto-mechanicalsystem, in accordance with one or more techniques of this disclosure.

FIG. 2 is a block diagram illustrating the circuit of FIG. 1 in furtherdetail, in accordance with one or more techniques of this disclosure.

FIG. 3 illustrates a conceptual diagram of the proof mass assembly ofFIG. 1 including a proof mass suspended within a frame by a firstdoubled ended tuning fork (DETF) structure, a second DETF structure, anda set of tethers, in accordance with one or more techniques of thisdisclosure.

FIG. 4 illustrates a conceptual diagram of the electro-opto-mechanicalsystem of FIG. 1, in accordance with one or more techniques of thisdisclosure.

FIG. 5 depicts additional aspects of the electro-opto-mechanical systemof FIG. 1, in accordance with one or more techniques of this disclosure.

FIG. 6 is a conceptual diagram illustrating example techniques forreducing drive feedthrough in optomechanical devices, in accordance withone or more techniques of this disclosure.

FIG. 7 is a conceptual diagram an example first optical response of afirst optical frequency component and a second optical frequencycomponent, in accordance with one or more techniques of this disclosure.

FIG. 8 is a conceptual diagram an example second optical response of afirst optical frequency component and a second optical frequencycomponent, in accordance with one or more techniques of this disclosure.

FIG. 9 is a conceptual diagram an example of an optical signal appliedto a proof mass assembly, in accordance with one or more techniques ofthis disclosure.

FIG. 10 is a conceptual diagram an example of an optical signalreflected output by a proof mass assembly in response to the opticalsignal of FIG. 9, in accordance with one or more techniques of thisdisclosure.

FIG. 11 is a conceptual diagram an example of a filtered optical signalresulting from filtering the optical signal of FIG. 10, in accordancewith one or more techniques of this disclosure.

FIG. 12 is a flow diagram illustrating an example for reducing drivefeedthrough in optomechanical devices, in accordance with one or moretechniques of this disclosure.

Like reference characters denote like elements throughout thedescription and figures.

DETAILED DESCRIPTION

This disclosure describes devices, systems, and techniques for reducingdrive feedthrough into the detection for optomechanical devices, suchas, for example, but not limited to, optomechanical accelerometers,electrical filters (e.g., high pass filters, low pass filters, and bandpass filters), strain sensors, pressure sensors, force sensors, andgyroscopes, where the structures have a coupled optical degree offreedom, and could help improve performance of such optomechanicaldevices. For example, in an optomechanical accelerometer, a resonancefrequency of a mechanical structure is shifted under acceleration in theoptomechanical device. The mechanical resonance frequency can bemeasured with an optical field by applying near-resonant light to thestructure's optical resonance and measuring the transmitted or reflectedlight (as the mechanical resonance frequency is imprinted as modulationof the phase and/or amplitude of the light by virtue ofoptical-mechanical coupling in the device). To increase the signal tonoise of the mechanical frequency measurement, systems may drive themechanical resonance to a larger amplitude by strongly amplitudemodulating the light field at or near the mechanical resonancefrequency, which may be referred to as a “driving modulation” of theinput optical field. In contrast, the “sense modulation” may refer to amodulation induced on the outgoing optical field by the mechanicalvibrations and can be less than, or even much less than, the drivingmodulation of the incoming driving optical field. In optomechanicaldevices in which a single laser field is used to both drive and sense,the outgoing sense optical field thus can have a deleterious“feed-through” modulation present on the optical field, which canfundamentally distort, obscure, or otherwise decreases the quality ofthe optical signal.

Techniques described herein may mitigate or help to eliminate distortionfrom feed-through modulation. In some examples, an optomechanicalaccelerometer may use one laser wavelength for the driving field andanother laser wavelength for the sensing field. The laser wavelength forthe driving field and the laser wavelength for the sensing field can beseparated through the use of wavelength selective optical components,such as, for example, but not limited to, filters or dichroics. Combinedwith appropriate readout and feedback system, techniques describedherein may provide a detection signal that is free of “feed-through,”can be locked to the mechanical resonance, and is advantageously almostfree or completely free of distortions or noise that is present insystems in which the feed-through has not be eliminated.

For example, the optomechanical device may include anelectro-opto-mechanical system configured to precisely measure very highacceleration values (e.g., up to 500,000 meters per second squared(m/s²)). The electro-opto-mechanical system may use a combination ofelectrical signals, optical signals, and mechanical signals to determinethe acceleration of the object.

An optomechanical device may be configured to measure the acceleration,velocity, vibration, etc. of the object in real-time or near real-time,such that processing circuitry may analyze the acceleration, velocity,vibration, etc. of the object over a period of time to determine apositional displacement of the object during the period of time. Forexample, the optomechanical device may be a part of an InertialNavigation System (INS) for tracking a position of an object based, atleast in part, on an acceleration of the object. Additionally, theoptomechanical device may be located on or within the object such thatthe optomechanical device accelerates, moves, vibrates, etc. with theobject. As such, when the object accelerates, moves, vibrates, etc., theoptomechanical device (including the mechanical assembly, proof massassembly, etc.) accelerates, moves, vibrates, etc. with the object. Insome examples, because acceleration over time is a derivative ofvelocity over time, and velocity over time is a derivative of positionover time, processing circuitry may, in some cases, be configured todetermine the position displacement of the object by performing a doubleintegral of the acceleration of the object over the period of time.Determining a position of an object using the accelerometer systemlocated on the object—and not using on a navigation system separate fromthe object (e.g., a Global Positioning System (GPS))—may be referred toas “dead reckoning.”

The optomechanical device may be configured to achieve high levels ofsensitivity in order to improve the accuracy of the acceleration,velocity, vibration, etc. values. High sensitivity may enable theoptomechanical device to detect very small acceleration, velocity,vibration, etc. values, detect a very small change in acceleration,velocity, vibration, etc. values, detect a large range of acceleration,velocity, vibration, etc. values, or any combination thereof.Additionally, an optomechanical device may be configured to accuratelydetermine the acceleration, velocity, vibration, etc. of the objectwhile the object is experiencing high levels of acceleration, velocity,vibration, etc. In this way, the an optomechanical device may beconfigured to enable an INS to accurately track the position of theobject while a magnitude of the acceleration, velocity, vibration, etc.of the object is very high.

The optomechanical device may, in some examples, include a MEMSaccelerometer which includes a light-emitting device, a circuit, and aproof mass assembly which includes a proof mass suspended within a frameby double-ended tuning fork (DETF) structures. In some examples, theoptomechanical device may include a single-ended tuning fork or anothermechanical assembly. For instance, the optomechanical device may use amechanical assembly suitable for electrical filters (e.g., high passfilters, low pass filters, and band pass filters), strain sensors,pressure sensors, force sensors, gyroscopes, or another mechanicalassembly.

In some examples, the DETF structures may be configured to guide opticalsignals. Additionally, optical signals may induce mechanical vibrationin the DETF structures. In some cases, acceleration causes adisplacement of the proof mass relative to the frame, the displacementaffecting mechanical vibration frequencies (e.g., mechanical resonancefrequencies) corresponding to the DETF structures. In this way, amathematical relationship may exist between acceleration and themechanical vibration frequencies of the DETF structures. As such, themathematical relationship may be leveraged to determine acceleration.The accelerometer device uses, in some examples, a combination ofoptical signals and electrical signals to measure the mechanicalvibration frequencies corresponding to the DETF structures and calculateacceleration based on the mechanical vibration frequencies.

While examples of an optomechanical device are described with respect toan example accelerometer, techniques described herein for noiserejection may be applied to optomechanical device configured to measurevarious parameters, including, but not limited to, acceleration,velocity, vibration, and other parameters. Moreover, while examples ofthe optomechanical device are described with respect to an example proofmass assembly that includes a DETF structure, other structures may beused, for example, but not limited to, a single-ended tuning forkstructure or another structure.

FIG. 1 is a block diagram illustrating an electro-opto-mechanical system10, in accordance with one or more techniques of this disclosure. FIG. 1is merely one non-limiting example system architecture that may utilizethe techniques of this disclosure for resonator stabilization. Asillustrated in FIG. 1, system 10 includes light-emitting devices 12A,12B (collectively, “light-emitting devices 12”), circuit 14, and proofmass assembly 16. Additionally, in the example illustrated in FIG. 1,circuit 14 includes electro-optic-modulators (EOM) 22A, 22B(collectively, “EOMs 22”), photoreceivers 24A, 24B (collectively,“photoreceivers 24”), feedback units 26A, 26B (collectively, “feedbackunits 26”), frequency counters 28A, 28B (collectively, “frequencycounters 28”), and processing circuitry 30. While the example of FIG. 1includes two EOMs, two photoreceivers, and two frequency counters, insome examples, an electro-opto-mechanical system may include only oneEOM, one photoreceiver, and one frequency counter or more than two EOMs,two photoreceivers, and two frequency counters.

In the example of FIG. 1, light-emitting device 12A, proof mass assembly16, EOM 22A, photoreceiver 24A, feedback unit 26A, and frequency counter28A form a first positive feedback loop. Additionally, in the example ofFIG. 1, light-emitting device 12B, proof mass assembly 16, EOM 22B,photoreceiver 24B, feedback unit 26B, and frequency counter 28B form asecond positive feedback loop. In some examples, the second positivefeedback loop may be omitted.

System 10 may be configured to determine an acceleration associated withan object (not illustrated in FIG. 1) based on a measured vibrationfrequency of a tuning fork structure of proof mass assembly. Forexample, system 10 may be configured to determine an accelerationassociated with an object (not illustrated in FIG. 1) based on ameasured vibration frequency of a set of double-ended tuning fork (DETF)structures which suspend a proof mass of proof mass assembly 16, wherethe vibration of the DETF structures is induced by an optical signalemitted by light-emitting device 12. In some examples, the firstpositive feedback loop generates a first frequency value representing avibration frequency of a first DETF structure and the second positivefeedback loop generates a second frequency value representing avibration frequency of a second DETF structure. Based on the firstvibration frequency and the second vibration frequency, system 10 maydetermine a first acceleration value and a second acceleration value,respectively. In some examples, system 10 determines an acceleration ofan object based on the first acceleration value and the secondacceleration value. In some examples, system 10 determines theacceleration of the object based on only the first acceleration value(e.g., the second positive feedback loop is omitted). In some examples,system 10 determines the acceleration of the object based on only thesecond acceleration value (e.g., the first positive feedback loop isomitted).

Light-emitting devices 12 may each include a laser device, also referredto herein as simply “laser,” configured to emit photons that form anoptical signal. In some examples, light-emitting devices 12 emit thephotons at an optical power within a range between 0.1 microwatts (μW)and 100 μW. In some examples, light-emitting devices 12 each include asemiconductor laser which includes a laser diode. In some examples, eachof light-emitting devices 12 may be configured to generate a firstoptical signal that interacts with proof mass assembly 16 and, inresponse to interacting with the proof mass assembly 16, is impressedwith one or more of a modulation in phase or frequency of mechanicalvibrations in proof mass assembly 16 and a second optical signal thatstimulates mechanical vibrations in proof mass assembly 16. In this way,the second optical signal (e.g., a driving optical signal) may providedriving modulation at proof mass assembly and feedback unit 26A may usethe first optical signal (e.g., a sense optical signal) that interactswith proof mass assembly 16 while the first optical signal drives themechanical vibration frequency at proof mass assembly 16.

In some examples, circuit 14 may include a set of electrical componentsfor processing and analyzing electrical signals received byphotoreceivers 24. Components of circuit 14 are described in furtherdetail below.

EOMs 22 may represent optical devices configured to modulate, based onelectrical signals produced and processed by circuit 14, an opticalsignal emitted by light-emitting device 12. EOM 22A, for example, mayinclude a set of crystals (e.g., Lithium Niobate crystals), where arefractive index of the set of crystals changes as a function of anelectric field proximate to the set of crystals. The refractive index ofthe crystals may determine a manner in which EOM 22A modulates theoptical signal. For example, the crystals of EOM 22A may receive theoptical signal from light-emitting device 12 while EOM 22A is alsoreceiving an electrical signal from feedback unit 26A of circuit 14. Assuch, the electrical signal may affect the electric field proximate tothe crystals of EOM 22A, thus causing EOM 22A to modulate the opticalsignal. In some examples, EOM 22A modulates the optical signal fordriving a mechanical response in proof mass assembly 16 by modulatingthe refractive index of the crystals using the electrical signal. EOM22A, in some cases, may transmit the modulated optical signal to proofmass assembly 16. In some examples, EOM 22B is substantially similar toEOM 22A, with EOM 22B controlled by an electrical signal from feedbackunit 26B.

Photoreceivers 24 (also referred to herein as “photodiodes”) may eachinclude one or more transistors configured to absorb photons of anoptical signal and output, in response to absorbing the photons, anelectrical signal. In this manner, photoreceivers 24 may be configuredto convert optical signals into electrical signals. Photoreceivers 24A,for example, may include a p-n junction that converts the photons of theoptical signal into the electrical signal, where the electrical signalpreserves at least some parameters of the optical signal. One or morefrequency values and intensity values associated with the optical signalmay be reflected in the electrical signal produced by photoreceivers 24Ain response to photoreceivers 24A receiving the optical signal. Forexample, photoreceivers 24A may produce a stronger electrical signal(e.g., greater current magnitude) in response to receiving a stronger(e.g., greater power) optical signal. Additionally, in some cases,photoreceivers 24A may produce the electrical signal to reflect the oneor more frequency values corresponding to the received optical signal.In other words, processing circuitry (e.g., processing circuitry 30) mayanalyze the electrical signal to determine the one or more frequencyvalues corresponding to the optical signal. Photoreceivers 24A mayinclude semiconductor materials such as any combination of IndiumGallium Arsenide, Silicon, Silicon Carbide, Silicon Nitride, GalliumNitride, Germanium, or Lead Sulphide. In some examples, photoreceivers24B is substantially similar to photoreceivers 24A.

Feedback units 26 may each include a set of circuit components forprocessing electrical signals. In some examples, the set of circuitcomponents included in feedback unit 26A may include any combination ofa band pass filter, a phase shifter, an electronic amplifier, and avoltage limiter. Such components may process, or filter, the electricalsignal such that certain aspects of the electrical signal may be moreefficiently measured (e.g., frequency values or intensity values). Inthe example of FIG. 1, feedback unit 26A may receive an electricalsignal from photoreceiver 24A and output a processed electrical signalto EOM 22A, frequency counter 28A, and light-emitting device 12A. Inthis way, feedback unit 26A acts as a part of a first positive feedbackloop by processing an electrical signal which EOM 22A uses to modulatean optical signal emitted by light-emitting device 12A, where themodulated optical signal passes through proof mass assembly 16 beforearriving back at circuit 14 for processing by feedback unit 26A.

Feedback unit 26B may be substantially similar to feedback unit 26A inthat feedback unit 26B receives an electrical signal from photoreceiver24B and delivers a processed electrical signal to frequency counter 28B,EOM 22B, and light-emitting device 12B. As such, feedback unit 26Boperates within a second feedback loop in a similar manner to whichfeedback unit 26A operates within the first feedback loop. Again,feedback unit 26B may be omitted.

Frequency counters 28 are circuit components that are each configuredfor measuring a frequency of an electrical signal. For example,frequency counter 28A may determine one or more frequency valuescorresponding to the processed electrical signal produced by feedbackunit 26A. Frequency counter 28A may measure frequency valuescorresponding to the processed electrical signal in real-time or nearreal-time, such that frequency counter 28A tracks the frequency valuesas a function of time. Frequency counter 28B may be substantiallysimilar to frequency counter 28A, except frequency counter 28B receivesan electrical signal from feedback unit 26B rather than from feedbackunit 26A.

Processing circuitry 30, and circuit 14 generally, may include one ormore processors that are configured to implement functionality and/orprocess instructions for execution within system 10. For example,processing circuitry 30 may be capable of processing instructions storedin a storage device (not illustrated in FIG. 1). Processing circuitry 30may include, for example, microprocessors, digital signal processors(DSPs), application specific integrated circuits (ASICs),field-programmable gate arrays (FPGAs), or equivalent discrete orintegrated logic circuitry, or a combination of any of the foregoingdevices or circuitry. Accordingly, processing circuitry 30 may includeany suitable structure, whether in hardware, software, firmware, or anycombination thereof, to perform the functions ascribed herein toprocessing circuitry 30. Processing circuitry 30, and circuit 14 mayinclude only analog circuitry, only digital circuitry, or a combinationof analog circuitry and digital circuitry. The term “processor” or“processing circuitry” may generally refer to any of the foregoinganalog circuitry and/or digital circuitry, alone or in combination withother logic circuitry, or any other equivalent circuitry.

Proof mass assembly 16 may include a proof mass, a frame, a set oftethers, and a set of DETF structures. The proof mass, in some examples,is suspended within the frame by the set of tethers and the set of DETFstructures. For example, proof mass assembly 16 may include a set ofDETF structures that suspend the proof mass in a first directionrelative to the frame. Additionally, the set of tethers may suspend theproof mass in a second direction and a third direction relative to theframe. The first direction, the second direction, and the thirddirection may represent three axes (e.g., x-axis, y-axis, and z-axis) ofa Cartesian space. In some cases, the set of DETF structures enable theproof mass to be displaced in the first direction. Additionally, in somecases, the set of tethers prevent the proof mass from being displaced inthe second direction and the third direction. In this way, proof massassembly 16 may only allow the proof mass to be displaced along a singleaxis (e.g., a displacement axis). Because the displacement of the proofmass may determine the acceleration measured by circuit 14, system 10may be configured to determine the acceleration relative to thedisplacement axis.

In some examples, the first positive feedback loop (e.g., light-emittingdevice 12A, proof mass assembly 16, EOM 22A, photoreceiver 24A, feedbackunit 26A, and frequency counter 28A) and the second positive feedbackloop (e.g., light-emitting device 12B, proof mass assembly 16, EOM 22B,photoreceiver 24B, feedback unit 26B, and frequency counter 28B) areconfigured to independently determine an acceleration valuerepresentative of an acceleration of an object including system 10. Forexample, light-emitting device 12 may emit an optical signal, EOM 22Amay modulate the optical signal for driving a mechanical response inproof mass assembly 16 to obtain a first modulated optical signal, andEOM 22A may transmit the first modulated optical signal to proof massassembly 16. Photoreceiver 24A may receive the first modulated opticalsignal from proof mass assembly 16, where properties of the firstmodulated optical signal received by photoreceiver 24A may be affectedby mechanical vibrations of a first DETF structure of proof massassembly 16. Photoreceiver 24A converts the first modulated opticalsignal into a first electrical signal and transmits the first electricalsignal to feedback unit 26A.

Feedback unit 26A may process the first electrical signal to obtain afirst processed electrical signal. For example, feedback unit 26A mayuse any combination of a first band pass filter, a first phase shifter,a first electronic amplifier, and a first voltage limiter to process thefirst electrical signal. Frequency counter 28A may receive the firstprocessed electrical signal and determine a first frequency valuecorresponding to the first processed electrical signal. In some cases,the first frequency value represents a mechanical vibration frequency ofthe first DETF structure of proof mass assembly 16, which carries thefirst modulated optical signal ultimately received by photoreceiver 24A.

In addition to transmitting the first processed electrical signal tofrequency counter 28A, feedback unit 26A may transmit the firstprocessed electrical signal to EOM 22A. In turn, EOM 22A may modulatethe optical signal emitted by light-emitting device 12 based on thefirst processed electrical signal, where the first modulated opticalsignal is transmitted to photoreceiver 24A via the first DETF structureof proof mass assembly 16, thus completing the first positive feedbackloop. As such, a future mechanical vibration frequency of the first DETFstructure depends, at least in part, on a current mechanical vibrationfrequency of the first DETF structure.

Additionally, in some examples, the second positive feedback loop maydetermine a second frequency value. For example, light-emitting device12 may emit an optical signal, EOM 22B may modulate the optical signalto obtain a second modulated optical signal, and EOM 22B may transmitthe second modulated optical signal to proof mass assembly 16.Photoreceiver 24B may receive the second modulated optical signal fromproof mass assembly 16, where properties of the second modulated opticalsignal received by photoreceiver 24B may be affected by mechanicalvibrations of a second DETF structure of proof mass assembly 16.Photoreceiver 24B converts the second modulated optical signal into asecond electrical signal and transmits the second electrical signal tofeedback unit 26B.

In some examples, feedback unit 26B processes the second electricalsignal to obtain a second processed electrical signal. For example,feedback unit 26B may use any combination of a second band pass filter,a second phase shifter, a second electronic amplifier, and a secondvoltage limiter to process the second electrical signal. Frequencycounter 28B may receive the second processed electrical signal anddetermine a second frequency value corresponding to the second processedelectrical signal. In some cases, the second frequency value representsa mechanical vibration frequency of the second DETF structure of proofmass assembly 16, which carries the second modulated optical signalultimately received by photoreceiver 24B.

In addition to transmitting the second processed electrical signal tofrequency counter 28B, feedback unit 26B may transmit the secondprocessed electrical signal to EOM 22B. In turn, EOM 22B may modulatethe optical signal for driving a mechanical response in proof massassembly 16 and emitted by light-emitting device 12 based on the secondprocessed electrical signal, where the second modulated optical signalis transmitted to photoreceiver 24B via the second DETF structure ofproof mass assembly 16, thus completing the second positive feedbackloop. As such, a future mechanical vibration frequency of the secondDETF structure depends, at least in part, on a current mechanicalvibration frequency of the second DETF structure.

Processing circuitry 30 may be configured to calculate, based on thefirst frequency value, a first acceleration value. In some examples, tocalculate the first acceleration value, processing circuitry 30 maysubtract a baseline frequency value from the first frequency value toobtain a first frequency difference value. The baseline frequency valuemay represent a resonant mechanical frequency of the first DETFstructure of proof mass assembly 16 while the proof mass is notdisplaced from a resting point along the proof mass displacement axis.In other words, the modulated optical signal emitted by EOM 22A mayinduce or drive the first DETF structure to vibrate at the baselinefrequency value while the proof mass is not displaced from the restingpoint along the proof mass displacement axis. As such, when the objectis not accelerating, the first frequency difference value may be equalto zero since the first acceleration value—which represents themechanical frequency of the first DETF structure—is equal to thebaseline frequency value when the proof mass is not displaced (e.g., theobject carrying system 10 is not accelerating). The first frequencydifference value, in some examples, may be correlated with anacceleration of the object. In other words, an increase of a magnitudeof the first frequency difference value may indicate an increase in theacceleration of the object and a decrease of a magnitude of the firstfrequency difference value may indicate decrease in the acceleration ofthe object.

Additionally, processing circuitry 30 may be configured to calculate asecond acceleration value based on the second acceleration value. Insome examples, to calculate the second acceleration value, processingcircuitry 30 may subtract a baseline frequency value from the secondfrequency value to obtain a second frequency difference value. Thesecond frequency difference value, in some examples, may be correlatedwith an acceleration of the object. In other words, an increase of amagnitude of the second frequency difference value may indicate anincrease in the acceleration of the object and a decrease of a magnitudeof the second frequency difference value may indicate decrease in theacceleration of the object. The first acceleration value and the secondacceleration value, which are calculated by processing circuitry 30,may, in some cases, be approximately equal.

FIG. 2 is a block diagram illustrating circuit 14 of FIG. 1 in furtherdetail, in accordance with one or more techniques of this disclosure. Asillustrated in FIG. 1, circuit 14 includes EOMs 22, photoreceivers 24,feedback units 26, frequency counters 28, and processing circuitry 30.Feedback units 26 may each include band pass filters 40A, 40B(collectively, “band pass filters 40”), phase shifters 42A, 42B(collectively, “phase shifters 42”), electronic amplifiers 44A, 44B(collectively, “electronic amplifiers 44), and drivers 47A, 47B(collectively, “drivers 47). The first feedback loop includes band passfilter 40A, phase shifter 42A, electronic amplifier 44A, and driver47A). The second feedback loop includes band pass filter 40B, phaseshifter 42B, electronic amplifier 44B, and driver 47B.

Circuit 14 may be configured to receive optical signals from proof massassembly 16, convert the optical signals into electrical signals,process the electrical signals, analyze the processed electrical signalsto determine acceleration values, and use the processed electricalsignals to modulate optical signals and reject noise, thus completingthe first feedback loop and the second feedback loop. While this exampleis an accelerometer, in some examples, circuit 14 may be configured toanalyze the processed electrical signals to determine other values, suchas, for example, but not limited to, velocity, vibration, rotation, andother values. For example, photoreceivers 24A may receive a firstmodulated optical signal from a first DETF structure of proof massassembly 16. The first modulated optical signal may include a frequencycomponent associated with the first DETF structure itself, such as avibration frequency of the first DETF structure. Photoreceivers 24A mayconvert the first modulated optical signal into a first set ofelectrical signals, preserving the frequency component indicative of thevibration frequency of the first DETF structure for driver 47A.Photoreceivers 24A may transmit the first set of electrical signals tofeedback unit 26A, which includes band pass filter 40A, phase shifter42A, electronic amplifier 44A, and driver 47A.

Band pass filter 40A may be an electronic filter that attenuatesfrequencies outside of a frequency range and “passes” frequencies withinthe frequency range. In some examples, band pass filter 40A includes anycombination of passive filters, active filters, infinite impulseresponse (IIR) filters, finite impulse response (FIR) filters,Butterworth filters, Chebyshev filters, elliptic filters, Besselfilters, Gaussian filters, Legendre filters, or Linkwitz-Riley filters.In some examples, band pass filter 40A includes a combination of a highpass filter which passes frequencies above a high pass cutoff point anda low pass filter which passes frequencies below a low pass cutoffpoint. In some cases, band pass filter 40A passes frequencies within arange between 100 kilohertz (kHz) and 10,000 kHz.

Phase shifter 42A may be configured to shift a phase of the firstelectrical signal and the second electrical signal. Phase may becharacterized as a position of an instant on a waveform cycle of aperiodic waveform. For example, the first electrical signal may includeperiodic waveforms which represent frequency components of the firstelectrical signal. A maximum peak of a sine wave for example, may be ata different phase than a minimum peak, or a zero crossing of the sinewave. In some examples, phase shifter 42A may “delay” the firstelectrical signal by a time value in order to shift a timeline in whichfrequency components of the first electrical signal oscillate and delaythe second electrical signal by a time value in order to shift atimeline in which frequency components of the second electrical signaloscillate.

Electronic amplifier 44A may amplify the first electrical signal and/orthe second electrical signal such that an amplitude of the firstelectrical signal is increased by a gain factor. In other words,electronic amplifier 44A may increase a power of the first electricalsignal and second electrical signal. By amplifying the first electricalsignal and second electrical signal using electronic amplifier 44A,circuit 14 may improve an ability of processing circuitry 30 to analyzethe first electrical signal and the second electrical signal, andmodulate the optical signal emitted by light-emitting device 12 usingEOM 22A.

Electronic amplifier 44A may include, in some cases, power amplifiers,operational amplifiers, or transistor amplifiers, or any combinationthereof. Additionally, in some examples, electronic amplifier 44A isconfigured to limit a voltage of the first electrical signal and/orsecond electrical signal to a maximum voltage value. In other words,electronic amplifier 44A may prevent the first electrical signal and thesecond electrical signal from exceeding the maximum voltage value,meaning that the first processed electrical signal and the secondprocessed electrical signal produced by feedback unit 26A may not exceedthe maximum voltage value.

In some examples, the first set of electrical signals may pass throughfeedback unit 26A in an order from band pass filter 40A, to phaseshifter 42A, to electronic amplifier 44A, and to driver 47A, asillustrated in FIG. 2. However, the order illustrated in FIG. 2 is notlimiting. Band pass filter 40A, phase shifter 42A, and electronicamplifier 44A may be arranged to process the first electrical signal andsecond first electrical signal in any order.

Driver 47A may be configured to cause EOM 22A to modulate the opticalsignal to drive a mechanical resonance of proof mass assembly 16. Forexample, driver 47A may be configured to generate a mechanical resonancefeedback signal that causes EOM 22A to operate near or at the mechanicalresonance of proof mass assembly 16. For example, driver 47A maygenerate the mechanical resonance feedback signal using a signalgenerator set to the mechanical resonance of proof mass assembly 16. Forexample, driver 47A may be designed to use a first optical signal (e.g.,a sensing optical signal) for sensing a mechanical resonance at proofmass assembly 16 while system 10 may use a second optical signal (e.g.,a driving optical signal) for driving the mechanical resonance at proofmass assembly 16.

Driver 47A may transmit a mechanical resonance feedback signal tofrequency counter 28A. Frequency counter 28A may determine a firstfrequency value, and processing circuitry 30 may determine a firstacceleration value based on the first frequency value. Additionally,driver 47A may transmit the mechanical resonance feedback signal to EOM22A and EOM 22A may modulate the optical signal for driving a mechanicalresponse and emitted by light-emitting device 12A based on themechanical resonance feedback signal generated based on a sensingoptical signal. In this way, proof mass assembly 16, photoreceiver 24A,band pass filter 40A, phase shifter 42A, electronic amplifier 44A,driver 47A, EOM 22A, and frequency counter 28A are a part of the firstpositive feedback loop which produces the first acceleration valueassociated with the object including system 10.

The components of feedback unit 26B (e.g., band pass filter 40B, phaseshifter 42B, electronic amplifier 44B, and driver 47B) may besubstantially similar to the respective components of feedback unit 26A.As such, the second positive feedback loop may be substantially similarto the first positive feedback loop.

FIG. 3 illustrates a conceptual diagram of proof mass assembly 16including a proof mass 50 suspended within a frame 52 by a first DETFstructure 54, a second DETF structure 58, and a set of tethers 62A-62R,in accordance with one or more techniques of this disclosure. Asillustrated in FIG. 3, proof mass assembly 16 includes proof mass 50,frame 52, first DETF structure 54 including a first pair of mechanicalbeams 56A, 56B (collectively, “first pair of mechanical beams 56”),second DETF structure 58 including a second pair of mechanical beams60A, 60B (collectively, “second pair of mechanical beams 60”), tethers62A-62R (collectively, “tethers 62”), first distal tine 64, and seconddistal tine 68. Proof mass assembly 16 is aligned relative to proof massdisplacement axis 72 and proof mass resting plane 74, as illustrated inFIG. 3.

Proof mass assembly 16 is a mechanical component ofelectro-opto-mechanical system 10. Because system 10 measuresacceleration, which is a rate in which a velocity of an object changesover time, it may be beneficial to include proof mass assembly 16 sothat acceleration can be measured based on a physical object such asproof mass 50. For example, system 10, which includes proof massassembly 16 may be fixed to or included within an object. Consequently,as the object accelerates at an acceleration value, proof mass assembly16 may also accelerate at the acceleration value. Acceleration mayaffect a position of proof mass 50 within frame 52 relative to proofmass displacement axis 72 and proof mass resting plane 74. For example,non-zero acceleration may cause proof mass 50 to be displaced from proofmass resting plane 74 along proof mass displacement axis 72. Asdescribed herein, if proof mass 50 is “displaced,” a center of mass ofproof mass 50 is displaced relative to frame 52. Increasing a magnitudeof acceleration may cause the displacement of proof mass 50 along proofmass displacement axis 72 to increase. Additionally, decreasing amagnitude of acceleration may cause the displacement of proof mass 50along proof mass displacement axis 72 to decrease.

In some examples, proof mass 50 takes the form of a patterned thin film,where the thin film has a mass within a range between 100 nanograms (ng)and 10,000 ng. Additionally, in some cases, the thin film has athickness within a range between 1 nm and 5,000 nm. Proof mass 50 may besuspended within frame 52 along proof mass displacement axis 72 by firstDETF structure 54 and second DETF structure 58 (collectively, “DETFstructures 54, 58”). First DETF structure 54 and second DETF structure58 may each have a high level of stiffness. For example, a scale factorof each of first DETF structure 54 and second DETF structure 58 may bewithin a range between 0.1 parts per million per gravitational forceequivalent (ppm/G) and 10 ppm/G. In this way, proof mass assembly 16 mayinclude a very light proof mass 50 which is secured by very stiff DETFstructures 54, 58. As such, a very high acceleration (e.g., 100,000m/s²) may cause proof mass 50 to be displaced along the proof massdisplacement axis 72 by a very small displacement value, for example. Insome examples, proof mass 50 is displaced along the proof massdisplacement axis 72 by a displacement value of up to 100 nm.

To generate acceleration values indicative of the acceleration of theobject in which system 10 is fixed to, system 10 may quantify, usingoptical signals, the displacement of proof mass 50 within frame 52. Toquantify the displacement of proof mass 50, system 10 may measure andanalyze mechanical properties of DETF structures 54, 58, such asmechanical vibrating frequency values corresponding to DETF structures54, 58. Indeed, since DETF structures 54, 58 suspend proof mass 50, themechanical vibrating frequencies of DETF structures 54, 58 may beaffected due to a displacement of proof mass 50. For example, adisplacement of proof mass 50 towards first DETF structure 54 and awayfrom second DETF structure 58 may cause proof mass 50 to apply acompression force to first DETF structure 54 and apply a tension forceto second DETF structure 58. Such a compression force may cause themechanical vibration frequency of first DETF structure 54 to decreaseand such a tension force may cause the mechanical vibration force ofsecond DETF structure 58 to increase. Changes in the mechanicalvibration frequencies of DETF structures 54, 58 may, in some examples,be proportional to the displacement of proof mass 50 relative to frame52 in the direction of proof mass displacement axis 72. In someexamples, System 10 may measure changes in the mechanical vibrationfrequencies of DETF structures 54, 58 by transmitting modulated opticalsignals through DETF structures 54, 58.

First DETF structure 54 may include, for example, the first pair ofmechanical beams 56 separated by a gap. The first pair of mechanicalbeams 56 may include photonic crystal mechanical beams that areconfigured for guiding a first modulated optical signal while first DETFstructure 54 is oscillating at a first mechanical vibrating frequency.In some cases, the first modulated optical signal is emitted bylight-emitting device 12 (illustrated in FIG. 1), and the firstmodulated optical signal itself induces vibration in first DETFstructure 54. Additionally, the vibration of the first DETF structure 54may affect certain properties of the first modulated optical signal suchthat the mechanical vibrating frequency of the first DETF structure 54is reflected in the first modulated optical signal. In this way, thefirst modulated optical signal may cause the mechanical vibration in thefirst DETF structure 54 and enable system 10 to measure the mechanicalvibration frequency of the first DETF structure 54 based on the firstmodulated optical signal.

Additionally, second DETF structure 58 may include, for example, thesecond pair of mechanical beams 60 separated by a gap. The second pairof mechanical beams 60 may include photonic crystal mechanical beamsthat are configured for guiding a second modulated optical signal whilesecond DETF structure 58 is oscillating at a second mechanical vibratingfrequency. In some cases, the second modulated optical signal is emittedby light-emitting device 12 (illustrated in FIG. 1), and the secondmodulated optical signal itself induces vibration in second DETFstructure 58. Additionally, the vibration of the second DETF structure58 may affect certain properties of the second modulated optical signalsuch that the mechanical vibrating frequency of the second DETFstructure 58 is reflected in the second modulated optical signal. Inthis way, the second modulated optical signal may cause the mechanicalvibration to occur in the second DETF structure 58 and enable system 10to measure the mechanical vibration frequency of the second DETFstructure 58 based on the second modulated optical signal.

Proof mass 50 may be fixed to frame 52 by tethers 62. In some examples,tethers 62 may suspend proof mass 50 in proof mass resting plane 74 suchthat the center of mass of proof mass 50 does not move within proof massresting plane 74 relative to frame 52. Proof mass displacement axis 72may represent a single axis (e.g., x-axis) of a Cartesian space, andproof mass resting plane 74 may represent two axes (e.g., y-axis andz-axis) of the Cartesian space. Since tethers 62 may restrict proof mass50 from being displaced relative to proof mass resting plane 74, in someexamples, proof mass 50 may only be displaced along the proof massdisplacement axis 72. System 10 may measure an acceleration based onmechanical vibrating frequencies of DETF structures 54, 58, where themechanical vibrating frequencies are related to an amount ofdisplacement of proof mass 50 along proof mass displacement axis 72. Inthis way, the acceleration determined by system 10 may be anacceleration relative to proof mass displacement axis 72.

First DETF structure 54 may include a proximal end that is proximate toproof mass 50, and a distal end that is separated from frame 52 by afirst gap 66. First distal tine 64 may help to suspend first DETFstructure 54 within frame 52 such that the first DETF structure 54 isperpendicular to proof mass resting plane 74. In some examples, firstdistal tine 64 extends perpendicularly to proof mass displacement axis72 between two sidewalls of frame 52. An optical signal may travelthrough frame 52 via a first optical fiber (not illustrated in FIG. 3),the optical signal being coupled across first gap 66 to first DETFstructure 54.

Second DETF structure 58 may include a proximal end that is proximate toproof mass 50, and a distal end that is separated from frame 52 by asecond gap 70. Second distal tine 68 may help to suspend first DETFstructure 58 within frame 52 such that the second DETF structure 58 isperpendicular to proof mass resting plane 74. In some examples, seconddistal tine 68 extends perpendicularly to proof mass displacement axis72 between two sidewalls of frame 52. An optical signal may travelthrough frame 52 via a second optical fiber (not illustrated in FIG. 3),the optical signal being coupled across second gap 70 to second DETFstructure 58.

FIG. 4 illustrates a conceptual diagram of system 10, in accordance withone or more techniques of this disclosure. The conceptual diagram ofFIG. 4 includes light-emitting devices 12, components of circuit 14, andproof mass assembly 16. In some examples, an object may be fixed tosystem 10. The object, in some cases, may accelerate. System 10,including proof mass assembly 16, may accelerate with the object. Asproof mass assembly 16 accelerates, proof mass 50 may be displacedrelative to frame 52. In the example illustrated in FIG. 4, if proofmass assembly 16 accelerates in direction 78, proof mass 50 is displacedin direction 78. Direction 78, in some examples, is aligned with a proofmass displacement axis (e.g., proof mass displacement axis 72 of FIG. 3.

As proof mass 50 is displaced in direction 78 relative to frame 52,proof mass 50 applies a compression force to first DETF structure 54,and proof mass 50 applies a tension force to second DETF structure 58.Such forces may affect mechanical vibrating frequencies of DETFstructures 54, 58, where mechanical vibration is induced in first DETFstructure 54 and second DETF structure 58 by electro-optic modulator 22Aand electro-optic modulator 22B, respectively. For example, thecompression force applied to first DETF structure 54 may cause themechanical vibration frequency of first DETF structure 54 to decrease,and the tension force applied to second DETF structure 58 may cause themechanical vibration frequency of second DETF structure 58 to increase.

Light-emitting devices 12 may emit a driving optical signal to EOMs 22and a sensing optical signal to proof mass assembly 16. For example,each of light-emitting devices 12 may be configured to generate asensing optical signal that interacts with proof mass assembly 16 and,in response to interacting with the proof mass assembly 16, is impressedwith one or more of a modulation in phase or frequency of mechanicalvibrations in proof mass assembly 16 and a driving optical signal thatis modulated by EOMs 22 and that stimulates mechanical vibrations inproof mass assembly 16. In this way, the driving optical signal mayprovide driving modulation at proof mass assembly and feedback unit 26A,26B may use the sensing optical signal that interacts with proof massassembly 16 while the driving optical signal drives the mechanicalvibration frequency at proof mass assembly 16.

In turn, EOM 22A and EOM 22B may modulate a respective driving opticalsignal according to a processed electrical signals produced by feedbackunit 26A and feedback unit 26B, respectively. As such, EOM 22A mayproduce a first modulated optical signal for driving a mechanicalresponse in proof mass assembly 16 and EOM 22B may produce a secondmodulated optical signal for driving a mechanical response in proof massassembly 16. EOM 22A, for example, may transmit the first modulatedoptical signal to proof mass assembly 16. The first modulated opticalsignal may cross frame 52. In some examples, frame 52 includes anaperture or another opening bridged by a first optical fiber whichallows the first modulated optical signal to pass. Additionally, thefirst modulated optical signal may couple across first gap 66 to thefirst DETF structure 54. The first modulated optical signal for drivinga mechanical response in proof mass assembly 16 may propagate throughfirst DETF structure 54, inducing mechanical vibration in first DETFstructure 54. In some examples, the first modulated optical signalpropagates the length of first DETF structure 54 towards proof mass 50along mechanical beam 56A and subsequently propagates the length offirst DETF structure 54 away from proof mass 50 along mechanical beam56B. In some examples, the first modulated optical signal propagates thelength of first DETF structure 54 towards proof mass 50 along mechanicalbeam 56B and subsequently propagates the length of first DETF structure54 away from proof mass 50 along mechanical beam 56A.

Similarly, the first sensing optical signal may cross frame 52. Thefirst sensing optical signal may couple across first gap 66 to the firstDETF structure 54. The first sensing optical signal may propagatethrough first DETF structure 54 to impress mechanical vibrations infirst DETF structure 54 onto the first sensing optical signal. In someexamples, the first sensing optical signal propagates the length offirst DETF structure 54 towards proof mass 50 along mechanical beam 56Aand subsequently propagates the length of first DETF structure 54 awayfrom proof mass 50 along mechanical beam 56B. In some examples, thefirst sensing optical signal propagates the length of first DETFstructure 54 towards proof mass 50 along mechanical beam 56B andsubsequently propagates the length of first DETF structure 54 away fromproof mass 50 along mechanical beam 56A. In any case, by propagating thelength of first DETF structure 54, the first sensing optical signal mayretain information indicative of mechanical properties (e.g., themechanical vibration frequency) of first DETF structure 54. After thefirst sensing optical signal propagates through first DETF structure 54,the first sensing optical signal may exit proof mass assembly 16 viafirst gap 66 and the first optical fiber of frame 52.

After exiting proof mass assembly 16, the first sensing optical signal,which may include fluctuations in amplitude and/or frequency, may arriveat photoreceiver 24A. Photoreceivers 24A convert the first modulatedoptical signal into a set of electrical signals for rejecting noise inlight-emitting device 12A and for driving EOM 22A to a mechanicalresonance of proof mass assembly 16. Frequency counter 28A may determinea first frequency value corresponding to the first processed electricalsignal, where the first frequency value is indicative of the mechanicalvibrating frequency of the first DETF structure 54. Processing circuitry30 may subtract a baseline frequency value from the first frequencyvalue to obtain a first frequency difference value and calculate a firstacceleration value based on the first frequency difference value. EOM22A may use the first processed electrical signal to modulate theoptical signal emitted by light-emitting device 12.

EOM 22B, for example, may transmit the second modulated optical signalto proof mass assembly 16. The second modulated optical signal may crossframe 52. In some examples, frame 52 includes an aperture or anotheropening bridged by a second optical fiber which allows the secondmodulated optical signal to pass. Additionally, the second modulatedoptical signal may couple across second gap 70 to the second DETFstructure 58. The second modulated optical signal may propagate throughsecond DETF structure 58, inducing mechanical vibration in second DETFstructure 58. In some examples, the second modulated optical signalpropagates the length of second DETF structure 58 towards proof mass 50along mechanical beam 60A and subsequently propagates the length ofsecond DETF structure 58 away from proof mass 50 along mechanical beam60B. In some examples, the second modulated optical signal propagatesthe length of second DETF structure 58 towards proof mass 50 alongmechanical beam 60B and subsequently propagates the length of secondDETF structure 58 away from proof mass 50 along mechanical beam 60A.

Similarly, the second sensing optical signal may cross frame 52.Additionally, the second sensing optical signal may couple across secondgap 70 to the second DETF structure 58. The second sensing opticalsignal may propagate through second DETF structure 58 to impressmechanical vibrations in first DETF structure 28 onto the second sensingoptical signal. In some examples, the second sensing optical signalpropagates the length of second DETF structure 58 towards proof mass 50along mechanical beam 60A and subsequently propagates the length ofsecond DETF structure 58 away from proof mass 50 along mechanical beam60B. In some examples, the second sensing optical signal propagates thelength of second DETF structure 58 towards proof mass 50 alongmechanical beam 60B and subsequently propagates the length of secondDETF structure 58 away from proof mass 50 along mechanical beam 60A. Inany case, by propagating the length of second DETF structure 58, thesecond sensing optical signal may retain information indicative ofmechanical properties (e.g., the mechanical vibration frequency) ofsecond DETF structure 58. After the second sensing optical signalpropagates through second DETF structure 58, the second sensing opticalsignal may exit proof mass assembly 16 via second gap 70 and the secondoptical fiber of frame 52.

After exiting proof mass assembly 16, the second sensing optical signal,which may include thermal noise, may arrive at photoreceivers 24B.Photoreceivers 24B convert the second modulated optical signal into aset of electrical signals for rejecting noise in light-emitting device12B and a second electrical signal for driving EOM 22B to a mechanicalresonance of proof mass assembly 16. Frequency counter 28B may determinea second frequency value corresponding to the second processedelectrical signal, where the second frequency value is indicative of themechanical vibrating frequency of the second DETF structure 58.Processing circuitry 30 may subtract a baseline frequency value from thesecond frequency value to obtain a second frequency difference value andcalculate a second acceleration value based on the second frequencydifference value. EOM 22B may use the second processed electrical signalto modulate the optical signal emitted by light-emitting device 12.

FIG. 5 depicts additional aspects of system 10, in accordance with oneor more techniques of this disclosure. For example, FIG. 5 illustratesthe first DETF structure 54 including the first pair of mechanical beams56. The optical signal emitted by light-emitting device 12 may induce aforce between the first pair of mechanical beams 56, and the force maybe modelled by a spring force. FIG. 5 illustrates a spring forceprovided by laser light between beams in an optical zipper in the gapbetween photonic crystal mechanical beams 56A, 56B of DETF structure 54(502), a perspective view depiction of vibration modes in beams in anoptical zipper in one common direction together (504), and a perspectiveview depiction of vibration modes in beams in an optical “zipper” inopposing directions of oscillation (506).

FIG. 6 is a conceptual diagram illustrating example techniques forreducing drive feedthrough in optomechanical devices, in accordance withone or more techniques of this disclosure. FIG. 6 is discussed withreference to FIGS. 1-5 for example purposes only. As shown,electro-opto-mechanical system 610, which may be an example of system10, may include light-emitting device 612, intensity stabilizer 617, EOM622, optical circulator 672, proof mass assembly 616 (also referred toherein as “device 616”), and feedback unit 626.

Light-emitting device 612 may include sense laser 611 and drive laser613. Sense laser 611 and drive laser 613 may be output at differentintensities. For example, sense laser 611 may be configured to generatea sensing optical signal such that the sense optical signal interactswith the proof mass assembly and, in response to interacting with theproof mass assembly, is impressed with one or more of a modulation inphase of mechanical vibrations in the proof mass assembly and afrequency of mechanical vibrations in the proof mass assembly. Incontrast, drive laser 613 may be configured to generate a drivingoptical signal such that the driving optical signal stimulatesmechanical vibrations in proof mass assembly 616. For instance, drivelaser 613 may be configured to generate the drive optical signal with anamplitude that is greater than ten times ( ) an amplitude of a senseoptical signal output by sense laser 611.

Sense laser 611 and drive laser 613 may be two intensity stabilizedlasers, each tuned to a slightly different frequency. For example, senselaser 611 may be tuned to vopt+Γ/4 and drive laser 613 may be tuned tovopt−Γ/4, where vopt is the optical resonance frequency and Γ is theFWHM. In another example, driver laser 613 may be tuned to vopt+Γ/4 andsense laser 611 may be tuned to vopt−Γ/4.

Sense laser 611 and drive laser 613 may be each tuned to a slightlydifferent frequency that is offset from the optical resonance frequency.For example, Sense laser 611 may be tuned to vopt+Γ/4+Δ and drive laser613 may be tuned to vopt+Γ/4−Δ, where Δ is a resolvable frequencydifference that is larger than the mechanical frequency. In someexamples, driver laser 613 may be tuned to vopt+Γ/4+Δ and sense laser611 may be tuned to vopt+Γ/4−Δ. In some examples, Sense laser 611 may betuned to vopt−Γ/4+Δ and drive laser 613 may be tuned to vopt−Γ/4−Δ. Insome examples, driver laser 613 may be tuned to vopt−Γ/4+Δ and senselaser 611 may be tuned to vopt−Γ/4−Δ, where vopt is the opticalresonance frequency and Γ is the FWHM.

Intensity stabilizer 617 may be configured to regulate an intensity ofthe optical signal output by sense laser 611 to regulate an intensity ofthe optical signal to a predetermined light intensity value. Forexample, the optical signal output by sense laser 611 passes through aVariable Optical Attenuator (VOA) 671, which may be configured toattenuate a portion of the optical signal. Tap 673 may be configured tooutput a first portion of the optical signal output from VOA 671 tophotodiode 675 and a second portion of the optical signal output fromVOA 671 to optical circulator 672. In this example, intensity servo 677may be configured to use an electrical signal output by photodiode 675to stabilize the overall light level of the optical signal.

Intensity stabilizer 617 may be configured to regulate an intensity ofthe optical signal output by drive laser 613 to regulate an intensity ofthe optical signal to a predetermined light intensity value. Forexample, the optical signal output by drive laser 613 passes through VOA686, which may be configured to attenuate a portion of the opticalsignal. Tap 676 may be configured to output a first portion of theoptical signal output from VOA 686 to photodiode 674 and a secondportion of the optical signal output from VOA 686 to optical EOM 622. Inthis example, intensity servo 677 may be configured to use an electricalsignal output by photodiode 674 to stabilize the overall light level ofthe optical signal.

Intensity servo 677 may be configured to regulate an intensity of theoptical signal output by sense laser 611 to a first predetermined lightintensity value before outputting the optical signal to proof massassembly 616. In some examples, intensity servo 677 may be configured toregulate an intensity of the optical signal output by drive laser 613 toa second predetermined light intensity value before outputting theoptical signal to proof mass assembly 616. In some examples, the secondpredetermined light intensity value may be larger (e.g., more than 10times, more than 20 times, etc.) than the first predetermined lightintensity value.

EOM 622 may be configured to modulate the optical signal output by tap676 (e.g., the driving optical signal) to an optical resonance of proofmass assembly 616. For example, EOM 622 may be configured to drive theoptical signal output by tap 676 to a peak optical resonance of proofmass assembly 616 using an electrical signal generated by feedback unit626.

Optical circulator 672 may be configured to output an optical signal(e.g., a driving optical signal) output by EOM 622 and an optical signaloutput (e.g., a sensing optical signal) by tap 673 to proof massassembly 616 and receive an optical signal reflected from proof massassembly 616. For example, an optical signal output by sense laser 611and stabilized by intensity stabilizer 617 and an optical signal outputby driver laser 613 and stabilized by intensity stabilizer 617 arecombined to generate a combined optical signal and the combined opticalsignal passes into port ‘1’ of optical circulator 672 and out of port‘2’ of optical circulator 672, where the modulated optical signalinteracts with proof mass assembly 616 (e.g., a zipper cavity measuredin reflection).

After reflection back into port ‘2’ of optical circulator 672, theoptical signal is output from port ‘3’ of optical circulator 672 tofeedback unit 626. Feedback unit 626 may be configured to use theoptical signal resulting from proof mass assembly 616 to drive themechanical response of proof mass assembly 616.

As shown, feedback unit 626 may include dichroic 684, photodiode 624A,624B (collectively, “photodiodes 624” (photodiode 624A is optional)),Band-Pass Filter (BPF) 620, frequency servo and data acquisition module628, and signal generator 646. Frequency servo and data acquisitionmodule 628 may be an example of drivers 47A, 47B.

Dichroic 648 may be configured to separate the drive and sense opticalsignals, which are at different wavelengths. For example, dichroic 648may be configured to output a first optical signal corresponding tovopt+Γ/4 and a second optical signal corresponding to vopt−Γ/4 or outputa first optical signal corresponding to vopt−Γ/4 and a second opticalsignal corresponding to vopt+Γ/4. In some examples, dichroic 648 may beconfigured to output a first optical signal corresponding to vopt+Γ/4+Δand a second optical signal corresponding to vopt+Γ/4−Δ or output afirst optical signal corresponding to vopt+Γ/4−Δ and a second opticalsignal corresponding to vopt+Γ/4+Δ. In some examples, dichroic 648 maybe configured to output a first optical signal corresponding tovopt−Γ/4+Δ and a second optical signal corresponding to vopt−Γ/4−Δ oroutput a first optical signal corresponding to vopt−Γ/4−Δ and a secondoptical signal corresponding to vopt−Γ/4+Δ.

Photodiode 624A may be configured to convert the first portion of theoptical signal output by dichroic 684 into a first electrical signal.Similarly, photodiode 624B may be configured to convert the secondportion of the optical signal output by dichroic 684 into a secondelectrical signal.

BPF 620 may be configured to pass electrical signals within a band offrequencies around the mechanical frequency of proof mass assembly 616.For example, BPF 620 may be configured to pass electrical signals withina band of frequencies at about 1 Mhz.

Frequency servo and data acquisition module 628 may be configured tocause EOM 622 to drive the optical signal output by tap 676 to amechanical resonance of proof mass assembly 616. For example, signalgenerator 646 may be configured to generate a mechanical resonancefeedback signal that causes EOM 622 to operate near or at the mechanicalresonance of proof mass assembly 616. For example, signal generator 646may generate a mechanical resonance feedback signal using signalgenerator 646 to set to the mechanical resonance of proof mass assembly616. Frequency servo and data acquisition module 628 may determine afirst frequency value to determine an acceleration value for proof massassembly 616. Frequency servo and data acquisition module 628 may beconfigured to measure, using the mechanical resonance feedback signal,an acceleration at proof mass assembly 616.

In accordance with techniques described herein, drive laser 613 may beconfigured to generate an optical signal that passes through EOM 622where light is modulated at the mechanical resonance frequency. Theoptical signal output by driver laser 613 is combined with an opticalsignal output by sense laser 611, and is a combination of the opticalsignal output by driver laser 613 and optical signal output by senselaser 611 is passed through optical circulator 672 to proof massassembly 616 (e.g., an optomechanical accelerometer, which may include aphotonic zipper cavity). The optical signal output by drive laser 613interacts with proof mass assembly 616 and stimulates mechanicalvibrations in proof mass assembly 616. The optical signal output bysense laser 611 interacts with proof mass assembly 616, and hasimpressed on the optical signal a modulation in phase and/or frequencydue to the mechanical vibrations simulated by the optical signal outputby drive laser 613, but also carrying information about the frequencyand phase of the mechanical vibrations, including, for example, one ormore shifts in the mechanical resonance due to acceleration of proofmass assembly 616. Both optical signals generated by sense laser 611 anddrive laser 613 leave proof mass assembly 616 (in reflection ortransmission). In the case of reflection, the optical signal is passedback through optical circulator 672 and to dichroic 684 with sufficientfrequency selectivity to separate the drive and sense optical fields,which are at different wavelengths. Photodiode 624B, BPF 620, frequencyservo and data acquisition module 628, and signal generator 646, may beconfigured to perform subsequent detection and processing of only theoptical signal output sense laser 611, thereby helping to providemeasure of acceleration which is not contaminated by feed-through. Inclosed loop oscillator operation, feedback unit 626 may be configured toelectronically detect and process the optical signal from sense laser611 and control signal generator 646 to drive the EOM 622 to create amodulated drive field. In some examples (e.g., open loop, or scanning,or Phase-Locked-Loop), feedback unit 626 may be configured to derive thesignal to be applied to EOM 622 from an independent frequencysynthesizer.

FIG. 7 is a conceptual diagram an example first optical response of afirst optical frequency component and a second optical frequencycomponent, in accordance with one or more techniques of this disclosure.FIG. 7 is discussed with reference to FIGS. 1-6 for example purposesonly. The abscissa axis (e.g., horizontal axis) of FIG. 7 representslaser wavelength in nanometers (nm) and the ordinate axis (e.g.,vertical axis) of FIG. 7 represents a normalized reflection 702. In theexample of FIG. 7, which may be useful for narrow optical resonances, alaser (e.g., drive laser or sense laser) may be set to first frequency704, which is tuned to vopt+Γ/4 and the other laser (e.g., sense laseror drive laser) is tuned to vopt−Γ/4, where vopt is the opticalresonance frequency and Γ is the FWHM.

FIG. 8 is a conceptual diagram an example second optical response of afirst optical frequency component and a second optical frequencycomponent, in accordance with one or more techniques of this disclosure.FIG. 8 is discussed with reference to FIGS. 1-7 for example purposesonly. The abscissa axis (e.g., horizontal axis) of FIG. 8 representslaser wavelength in nanometers (nm) and the ordinate axis (e.g.,vertical axis) of FIG. 8 represents a normalized reflection 802. In theexample of FIG. 8, a laser (e.g., drive laser or sense laser) may be setto first frequency 804, which is tuned to vopt+Γ/4−Δ and the other laser(e.g., sense laser or drive laser) is tuned to vopt+Γ/4+Δ, where vopt isthe optical resonance frequency and Γ is the FWHM. In some examples, alaser (e.g., drive laser or sense laser) may be set to first frequency,which is tuned to vopt−Γ/4−Δ and the other laser (e.g., sense laser ordrive laser) is tuned to vopt−Γ/4+Δ, where vopt is the optical resonancefrequency and Γ is the FWHM.

FIG. 9 is a conceptual diagram an example of an optical signal appliedto a proof mass assembly, in accordance with one or more techniques ofthis disclosure. FIG. 9 is discussed with reference to FIGS. 1-8 forexample purposes only. The abscissa axis (e.g., horizontal axis) of FIG.9 represents laser wavelength in nanometers (nm) and the ordinate axis(e.g., vertical axis) of FIG. 9 represents a normalized reflection 902.In the example of FIG. 9, optical signal 912 corresponds to an opticalsignal output by drive laser 613 before output to optical circulator 672and after processing by intensity stabilizer 617 and optical signal 914corresponds to an optical signal output by sense laser 611 before outputto optical circulator 672 and after processing by intensity stabilizer617.

As shown, optical signal 912 includes a central frequency withdeleterious “feed-through” modulation, which may be represented as alower sideband and an upper sideband. Optical signal 914, however,includes a central frequency with little or no deleterious feed-throughmodulation.

FIG. 10 is a conceptual diagram an example of an optical signalreflected output by a proof mass assembly in response to the opticalsignal of FIG. 9, in accordance with one or more techniques of thisdisclosure. FIG. 10 is discussed with reference to FIGS. 1-9 for examplepurposes only. The abscissa axis (e.g., horizontal axis) of FIG. 10represents laser wavelength in nanometers (nm) and the ordinate axis(e.g., vertical axis) of FIG. 10 represents a normalized reflection1002. In the example of FIG. 10, optical signal 1012 corresponds to anoptical signal output by drive laser 613 before output to dichroic 684and after output by optical circulator 672 and optical signal 1014corresponds to an optical signal output by sense laser 611 before outputto dichroic 684 and after output by optical circulator 672.

As shown, optical signal 1012 includes a central frequency withdeleterious feed-through modulation after interacting with proof massassembly 616. Accordingly, while optical signal 1012 includes animpression from interactions with proof mass assembly 616, theimpression is obscured by the deleterious feed-through modulationassociated with driving the mechanical response at proof mass assembly.In contrast, optical signal 1014 includes a central frequency with smallor no deleterious feed-through modulation. As such, optical signal 1014more clearly includes the impression from interactions with proof massassembly 616, which can be seen as additional sidebands, compared tooptical signal 1012.

FIG. 11 is a conceptual diagram an example of a filtered optical signalresulting from filtering the optical signal of FIG. 10, in accordancewith one or more techniques of this disclosure. FIG. 11 is discussedwith reference to FIGS. 1-10 for example purposes only. The abscissaaxis (e.g., horizontal axis) of FIG. 11 represents laser wavelength innanometers (nm) and the ordinate axis (e.g., vertical axis) of FIG. 11represents a normalized reflection 1102. In the example of FIG. 11,optical signal 1114 corresponds to an optical signal output by senselaser 611 after processing by dichroic 684.

FIG. 12 is a flow diagram illustrating an example for reducing drivefeedthrough in optomechanical devices, in accordance with one or moretechniques of this disclosure. FIG. 12 is discussed with reference toFIGS. 1-11 for example purposes only.

Light-emitting device 612 generates a first optical signal and a secondoptical signal (1202). In some examples, the first optical signalcomprises a frequency different than a frequency of the second opticalsignal. EOM 622 modulates the second optical signal (1204). Opticalcirculator 672 outputs the first optical signal and the second opticalsignal to the proof mass assembly (1206). Dichroic 684 generates afiltered optical signal corresponding to a response by the proof massassembly to the first optical signal without the second optical signal(1208). Photodiode 624B generates an electrical signal based on thefiltered optical signal (1210). In some examples EOM 622 modulates thesecond optical signal based on the electrical signal.

Frequency servo and data acquisition module 628 may optionally generatean indication of acceleration at the proof mass assembly based on theelectrical signal (1212). However, in other examples, circuitry maygenerate other indications, such as, for example, an indication ofvelocity, vibration, rotation, position, or another indication at amechanical assembly.

The optomechanical device described herein may include only analogcircuitry, only digital circuitry, or a combination of analog circuitryand digital circuitry. Digital circuitry may include, for example, amicrocontroller on a single integrated circuit containing a processorcore, memory, inputs, and outputs. For example, digital circuitry of theoptomechanical device described herein may include one or moreprocessors, including one or more microprocessors, digital signalprocessors (DSPs), application specific integrated circuits (ASICs),field programmable gate arrays (FPGAs), or any other equivalentintegrated or discrete logic circuitry, as well as any combinations ofsuch components. The term “processor” or “processing circuitry” maygenerally refer to any of the foregoing analog circuitry and/or digitalcircuitry, alone or in combination with other logic circuitry, or anyother equivalent circuitry.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses that include integrated circuits (ICs) or setsof ICs (e.g., chip sets). Various components, modules, or units aredescribed in this disclosure to emphasize functional aspects of devicesconfigured to perform the disclosed techniques, but do not necessarilyrequire realization by different hardware units. Rather, various unitsmay be combined or provided by a collection of interoperative hardwareunits, including one or more processors as described above, inconjunction with suitable software and/or firmware.

What is claimed is:
 1. An optomechanical device for producing anddetecting optical signals, the device comprising: a proof mass assembly;one or more laser devices comprising: a sense laser device configured togenerate a first optical signal at a frequency corresponding to one ofan optical resonance of the proof mass assembly plus one quarter of aFull Width at Half Maximum (FWHM) of the optical resonance of the proofmass assembly, the optical resonance of the proof mass assembly minusone quarter of the FWHM of the optical resonance of the proof massassembly, the optical resonance of the proof mass assembly plus onequarter of the FWHM of the optical resonance of the proof mass assemblyplus an offset, or the optical resonance of the proof mass assemblyminus one quarter of the FWHM of the optical resonance of the proof massassembly minus the offset; and a drive laser device configured togenerate a second optical signal at a frequency corresponding to one ofthe optical resonance of the proof mass assembly minus one quarter ofthe FWHM of the optical resonance of the proof mass assembly, theoptical resonance of the proof mass assembly plus one quarter of theFWHM of the optical resonance of the proof mass assembly, the opticalresonance of the proof mass assembly plus one quarter of the FWHM of theoptical resonance of the proof mass assembly minus an offset, or theoptical resonance of the proof mass assembly minus one quarter of theFWHM of the optical resonance of the proof mass assembly plus theoffset, wherein the first optical signal comprises a frequency differentthan a frequency of the second optical signal; and circuitry configuredto: modulate, with an electro-optic modulator (EOM), the second opticalsignal; output the first optical signal and the second optical signal tothe proof mass assembly; generate a filtered optical signalcorresponding to a response by the proof mass assembly to the firstoptical signal without the second optical signal; and generate anelectrical signal based on the filtered optical signal, wherein the EOMmodulates the second optical signal based on the electrical signal. 2.The optomechanical device of claim 1, wherein the circuitry isconfigured to: generate an indication of an acceleration at the proofmass assembly based on the electrical signal.
 3. The optomechanicaldevice of claim 1, wherein the sense laser device is configured togenerate the first optical signal such that the first optical signalinteracts with the proof mass assembly and, in response to interactingwith the proof mass assembly, is impressed with one or more of amodulation in phase of mechanical vibrations in the proof mass assemblyand a frequency of mechanical vibrations in the proof mass assembly; andwherein the drive laser device is configured to generate the secondoptical signal such that the second optical signal stimulates mechanicalvibrations in the proof mass assembly.
 4. The optomechanical device ofclaim 1, wherein the drive laser device is configured to generate thesecond optical signal with an amplitude that is greater than ten timesan amplitude of the first optical signal.
 5. The optomechanical deviceof claim 1, wherein the sense laser device is configured to generate thefirst optical signal at a frequency corresponding to the opticalresonance of the proof mass assembly plus one quarter of the FWHM of theoptical resonance of the proof mass assembly and wherein the drive laserdevice is configured to generate the second optical signal at afrequency corresponding to the optical resonance of the proof massassembly minus one quarter of the FWHM of the optical resonance of theproof mass assembly; or wherein the sense laser device is configured togenerate the first optical signal at a frequency corresponding to theoptical resonance of the proof mass assembly minus one quarter of theFWHM of the optical resonance of the proof mass assembly and wherein thedrive laser device is configured to generate the second optical signalat a frequency corresponding to the optical resonance of the proof massassembly plus one quarter of the FWHM of the optical resonance of theproof mass assembly.
 6. The optomechanical device of claim 1, whereinthe sense laser device is configured to generate the first opticalsignal at a frequency corresponding to the optical resonance of theproof mass assembly plus the summation of one quarter of the FWHM of theoptical resonance of the proof mass assembly and an offset and whereinthe drive laser device is configured to generate the second opticalsignal at a frequency corresponding to the optical resonance of theproof mass assembly plus a result of subtracting the offset from the onequarter of the FWHM of the optical resonance of the proof mass assembly;or wherein the sense laser device is configured to generate the firstoptical signal at a frequency corresponding to the optical resonance ofthe proof mass assembly plus a result of subtracting one quarter of theFWHM of the optical resonance of the proof mass assembly subtracted fromthe offset and wherein the drive laser device is configured to generatethe second optical signal at a frequency corresponding to the opticalresonance of the proof mass assembly minus a result of summing onequarter of the FWHM of the optical resonance of the proof mass assemblyand the offset.
 7. The optomechanical device of claim 6, wherein theoffset is a frequency that is larger than a mechanical frequency of theproof mass assembly.
 8. The optomechanical device of claim 1, whereinthe circuit comprises an optical circulator, wherein, to output thefirst optical signal and the second optical signal to the proof massassembly, the circuit is configured to: combine the first optical signaland second optical signal into a combined optical signal; output thecombined optical signal to the optical circulator, wherein the opticalcirculator outputs the combined optical signal to the proof massassembly and receives a response from the proof mass assembly to thefirst optical signal and the second optical signal.
 9. Theoptomechanical device of claim 8, wherein the circuit comprises a filterconfigured to: generate the filtered optical signal corresponding to theresponse by the proof mass assembly to the first optical signal withoutthe second optical signal using the response from the proof massassembly to the first optical signal and the second optical signal. 10.The optomechanical device of claim 9, wherein the filter is a dichroic.11. The optomechanical device of claim 1, wherein, to modulate thesecond optical signal, the circuit is configured to: apply a band passfilter to the first electrical signal to generate a filtered electricalsignal; estimate a frequency of a mechanical resonance of the proof massassembly using the filtered electrical signal; drive a signal generatorusing the estimated frequency of the mechanical resonance of the proofmass assembly to generate a mechanical resonance feedback signal; anddrive the EOM using the mechanical resonance feedback signal.
 12. Theoptomechanical device of claim 11, wherein the proof mass assemblycomprises a set of double-ended tuning fork (DETF) structures andwherein the mechanical resonance of the proof mass assembly is amechanical resonance of the DETF structures.
 13. The optomechanicaldevice of claim 1, wherein the filtered response is a first filteredresponse, wherein the electrical signal is a first electrical signal,and wherein the circuitry is further configured to: generate a secondfiltered optical signal corresponding to a response by the proof massassembly to the second optical signal without the first optical signal;and generate a second electrical signal based on the second filteredoptical signal.
 14. The optomechanical device of claim 1, wherein thecircuit is configured to: regulate an intensity of the first opticalsignal to a first predetermined light intensity value before outputtingthe first optical signal and the second optical signal to the proof massassembly; and regulate an intensity of the second optical signal to asecond predetermined light intensity value before outputting the firstoptical signal and the second optical signal to the proof mass assembly.15. A method for producing and detecting optical signals, the methodcomprising: generating, by a sense laser device of one or more laserdevices, a first optical signal at a frequency corresponding to one ofan optical resonance of a proof mass assembly plus one quarter of a FullWidth at Half Maximum (FWHM) of the optical resonance of the proof massassembly, the optical resonance of the proof mass assembly minus onequarter of the FWHM of the optical resonance of the proof mass assembly,the optical resonance of the proof mass assembly plus one quarter of theFWHM of the optical resonance of the proof mass assembly plus an offset,or the optical resonance of the proof mass assembly minus one quarter ofthe FWHM of the optical resonance of the proof mass assembly minus theoffset; generating, by a drive laser device of the one or more laserdevices, a second optical signal at a frequency corresponding to one ofthe optical resonance of the proof mass assembly minus one quarter ofthe FWHM of the optical resonance of the proof mass assembly, theoptical resonance of the proof mass assembly plus one quarter of theFWHM of the optical resonance of the proof mass assembly, the opticalresonance of the proof mass assembly plus one quarter of the FWHM of theoptical resonance of the proof mass assembly minus an offset, or theoptical resonance of the proof mass assembly minus one quarter of theFWHM of the optical resonance of the proof mass assembly plus theoffset, wherein the first optical signal comprises a frequency differentthan a frequency of the second optical signal; modulating, by anelectro-optic modulator (EOM) of circuitry, the second optical signal;outputting, by the circuitry, the first optical signal and the secondoptical signal to the proof mass assembly; generating, by the circuitry,a filtered optical signal corresponding to a response by the proof massassembly to the first optical signal without the second optical signal;and generating, by the circuitry, an electrical signal based on thefiltered optical signal, wherein the EOM is configured to modulate thesecond optical signal based on the electrical signal.
 16. The method ofclaim 15, further comprising: generating, by the circuitry, anindication of an acceleration at the proof mass assembly based on theelectrical signal.
 17. The method of claim 15, wherein the sense laserdevice is configured to generate the first optical signal such that thefirst optical signal interacts with the proof mass assembly and, inresponse to interacting with the proof mass assembly, is impressed withone or more of a modulation in phase of mechanical vibrations in theproof mass assembly and a frequency of mechanical vibrations in theproof mass assembly; and wherein the drive laser device is configured togenerate the second optical signal such that the second optical signalstimulates mechanical vibrations in the proof mass assembly.
 18. Anoptomechanical system for producing and detecting optical signals, theoptomechanical device comprising: one or more laser devices comprising:a sense laser device configured to generate a first optical signal at afrequency corresponding to one of an optical resonance of a mechanicalassembly plus one quarter of a Full Width at Half Maximum (FWHM) of theoptical resonance of the mechanical assembly, the optical resonance ofthe mechanical assembly minus one quarter of the FWHM of the opticalresonance of the mechanical assembly, the optical resonance of themechanical assembly plus one quarter of the FWHM of the opticalresonance of the mechanical assembly plus an offset, or the opticalresonance of the mechanical assembly minus one quarter of the FWHM ofthe optical resonance of the mechanical assembly minus the offset; and adrive laser device configured to generate a second optical signal at afrequency corresponding to one of the optical resonance of themechanical assembly minus one quarter of the FWHM of the opticalresonance of the mechanical assembly, the optical resonance of themechanical assembly plus one quarter of the FWHM of the opticalresonance of the mechanical assembly, the optical resonance of themechanical assembly plus one quarter of the FWHM of the opticalresonance of the mechanical assembly minus an offset, or the opticalresonance of the mechanical assembly minus one quarter of the FWHM ofthe optical resonance of the mechanical assembly plus the offset,wherein the first optical signal comprises a frequency different than afrequency of the second optical signal; and a circuit configured to:modulate, with an electro-optic modulator (EOM), the second opticalsignal; output the first optical signal and the second optical signal toa mechanical assembly; generate a filtered optical signal correspondingto a response by the mechanical assembly to the first optical signalwithout the second optical signal; and generate an electrical signalbased on the filtered optical signal, wherein the EOM modulates thesecond optical signal based on the electrical signal.